Method of making spark-plug casings



Nov( 2 1926.

H RABEZZANA METHOD OF MAKING SPARK PLUG CASINGS Fi led May 15, 1922 Patented Nov. 2, 1926.

'uirsn STATES HECTOR BABIEZZANA, OF FLINT, MICHIGAN, ASSIGNOR TO A C SPAR-K PLUG COMPANY,

OF FLINT, MICHIGAN, A CGRPORATION OF MICHIGAN.

METHOD OF MAKING Application filed May 15,

My invention relates to spark plugs such as are used in internal combustion engines to ignite the mixture supplied thereto, and

- particularly to spark plugs of the type or 5 class having a hollow shell or casing within which the insulating member of the plug is held in place, one of the sparking terminals or electrodes of the plug being supported from the hollow shell or casing, and the other being carried by the insulating memher which is secured in place within said shell; and the object of my invention is to provide an improved method or process of making the metallic shells or casings of such plugs and by the use of which process the cost of manufacturing thereof is materially reduced, while at the same time a better shell or casing and a better plug is secured.

More specifically stated the object of my invention is to provide a metallic shell or casing for spark plugs of the type referred to and wherein the usual threads, whereby the plug is screwed into an opening in an engine cylinder provided for it, are formed thereon by rolling said threads into the exterior surface of a portion of the casing provided to receive them; thus materially reducing the cost of the casing, and providing a casing which may be produced much more rapidly than has heretofore commonly been the case; as the threads may be rolled into or upon an article to be threaded more rapidly and at much less expense than is the case in cutting threads with an ordinary cutting tool andby the use of a screw machine, or by other processes which remove material from the shell by cutting tools in forming the thread. f

In the art relating to the. rolling of threads upon or into articles to be threaded it has heretofore been regarded as difficult, if not impossible, to form such threads upon a hollow or tubular member; as the process of rolling threads subjects the article being threaded to severe crushing and other forces tending to distort it. Inasmuch, therefore, as the casing members of spark plugs are hollow to provide for the insulating member of the plug it has been deemed impossible to form threads thereupon by the thread rolling process because of the crushing forces to which the shell is subjected-and the distortion incident to the action ofthe SPARK-PLUG oAsINGs.

1922 Serial No. 561,072.

dies employed in forming threads by the thread rolling process.

My invention, therefore, contemplates the strengthening of the tubular blank from which the casing is formed in such a manner and to such an extent that it will resist the crushing, twisting and other stresses incident to rolling threads thereupon; the strengthening being commonly secured by v leaving end walls in the blanks from which the shells are eventually formed, or, as otherwise stated, by boring part way only into and along the length of solid or bar stock from which each individual blank is formed, by the use of an ordinary turret lathe or s serves to prevent crushing of the tubular portion of the shell as threads are subsequently rolled thereupon. Afterwards the shell is finished by removing said end'wall in any suitabl'e'way as by boring or punching it out, the same having served the purpose of strengthening the casing blank during the thread rolling operation, thus completing the shell or casing of the plug.

The drawing accompanying and forming a part of this specification illustrates in a conventional manner a machine capable of 'use for rolling threads upon a portion of a spark plug casing to be threaded; although it will be appreciated that my invention relates to the method of threading spark plug casings by rolling threads thereupon, and to a casing member having threads provided thereupon by the thread rolling process, and is independent of the particular machine'or device employed in forming the threads.

. In' the drawing:

Figure 1 is a view showing a thread rolling machine'capable of use in performing my invention, the view being largely of a conventional character.

Figure 2 is a view showing one of the two dies whereby threads are rolled upon the casing member or blank, upon a larger scale than in Figure 1.

Figure 3 is a view showing a section upon a plane indicated substantially by the line 33, Figure 1, allelements other than the dies and the casingoperated upon being omitted, this view being upon a considerably larger scale than Figure 1.

Figure 4 is a view upon a vertical central crew machine, and which end wall plane showing a finished spark plug shell or casing made in accordance with my invention.

Figure 5 is a view similar to Figure &, but showing a complete spark plug.

Referring now to the drawing, thereterence numeral 5 designates a suitable frame structure adapted to support the various parts or elements of a machine capable of rolling threads upon the exterior of spark plug shells or casings, and 6 designatesa reciprocating die carrier movable in suitable guides carried by the frame; said carrier being operated from a rotating shaft 7 and a crank disk 8 through a suitable connecting rod 9 pivotally connected with, said carrier and with said crank disk, as will be understood irom Figrirel, l l' The reciprocating carrier 6 serves as av support for one o't the two thread rolling dies 10 of theinachine, theother' d-ie'being indicated same being held in'aii ied'position relative to the frame of themachine. These dies 10, 11 move alongside and parallel with one another a short distance apart and roll the shell or casing blank 12 between them from right to left, referring to Figure 1, during which threads are formed upon the periphery of the lower portion of: the shell; these dies being provided with inclined grooves 13, as shown'in FigureQ, of the usual form employed in thread rolling machines.

The elements thus far described are the usual elements commonly present in thread rolling machines and my invention is in no way concerned with them except to the extent that such elements, or their equivalents, are employed in providing threads: upon spark plug casings made in accordance with my invention.

The member or element designated by the numeral 12 is referred to as a casing member or blank because oi the act that it is in an uncoi'npleted and unfinished form at the time when the threads are formed thereupon by the machine above referred to or by an equivalent device. These casing members or blanks are commonly formed from solid bar stock by boring out the interior thereof, as shown at 14- 15, inorder to provide a hollow casing or one having an internal space or cavity within which the insuljating member 18 of the plug is held. i i

In forming spark plug casings in accordance with my invention the boring out of the insulator receiving chamber 11 l15 is arrested at such a time as toleavea closed head or end wall at the inner end of the plug, as indicated at 16, which closed end serves to strengthen the hollow portion. 17 of the shell blank upon which the threads are toibe formed; and a'ctsto prevent distortion of said portion'by twisting stresses, as'welll also as the crushing 0t porti' by referencenumeral lland the,

during the thread rolling operation in which the portion of the shell operated upon is subjected to unusually severe stress which would injure or crush it were it not for the strengthening element or member provided by the closed end 16 of the shell blank.

lit will be appreciated, however, that the internal strengthening element provided for supporting the side walls 01 the tubular portions oi the blank during the thread rolling operation may be otherwise provided and diilerently. located within the same as the dominant idea of my invention is to strengthen the tubular and comparatively weak portion 01' the shell blank by any internal strengthening element of such form, and solocated', as to eiiectively support the walls of the tubularlportion during the formation of the threads thereon by the thread rolling rocess? As above stated, the shell blanks are operated upon by'th e thread rolling machine while thefstrengthening element "formed by the closed head 16', or its equivalent, remains a part of the shell, and while the shell is in an unfinished condition, Thereafter, and after the threads have. been properly formed, this end wall or strengthening element is removed from the casing member by punching, drilling, broaching, or equivalent process, to iinish the Shell; the completed shell being hollow and havinga passage extending therethrough, as shown in Figure 4, in order that the insulating member 18 may be properly held in place and the inner electrode which extends through the insulating member may be disposed in sparking relation to the grounded or shell electrode of the plug, as will be understood from Figure 5.

Having thus described and explained my invention, I claim and desire to secure by Letters Patent:

1/ The method of making a metallic shell or casing for a spark plug which consists in providing a hollow casing member or blank having an internal strengthening element integral therewith and adapted to prevent distortion of said member during a thread forming operation; forming a thread upon the exterior of said member adjacent said strengthening element; and removing said strengthening element from the casing 1nember to complete the casing,

2. The methodof making a metallic shell creasing fora spark plug which consists in l providing a hollow casing member or blank having an internal strengthening element integral therewith and located adjacent a pormeter the blank which is to be exteriorly threaded, forming a thread upon the exterior of the blank adjacent said strengthening element; and removing 'said'strengthening element from the blank to complete the or casing for a spark plug which consists in providing a hollow casing member or blank having an internal strengthening element integral therewith and located adjacent a portion of the blank which is to be externally threaded; operating upon said exterior portion by thread forming dies which tend to distort the same; and removing said strengthening element from the blank to complete the casing.

4. The method of making a metallic shell or casing for a spark plug which consists in providing a hollow casing member or blank having an internal strengthening element integral therewith and located adjacent a portion thereof to be exteriorly threaded; rolling threads upon the exterior of the blank adjacent said strengthening element; and removing said strengthening element from the blank to complete the casing.

5. The method of making a metallic shell or casing for a spark plug which consists in providing a hollow casing member or blank with an internal strengthening element integral therewith and located adjacent a portion 01 the blank which is to be externally threaded; rolling said casing member between dies movable longitudinally relative to one another and adapted to roll a thread upon the exterior of said member; and removing said strengthening element from said casing member to complete the casing.

6. The method oi making a metallic shell or casing for a spark plug which consistsin providing a hollow casing member or blank strengthening element is located; and removing said strengthening element from the blank to complete the casing.

7. The method of making a metallic shell or casing for a spark plug which consists in providing a hollow casing member or blank having a closed end integral with and located adjacent the portion thereof to be ex ternally threaded; operating upon said exterior portion by thread forming dies tending to distort said casing to thereby provide an exterior thread adjacent said closed end; and removing said closed end from the blank to complete the casing.

8. The method of making a metallic shell or casing for a spark plug which consists in providing a hollow casing member or blank of a form adapted to resist crushing as threads are rolled thereupon; rolling threads upon an exterior portion of said blank; and further operating upon said blank subsequent to the rolling of the threads thereupon by removing a part thereof which resists the crushing of the threads to impart to it the form of a finished casing.

In testimony whereof I affix my signature.

HECTOR RABEZZANA. 

